As with any aftermarket part, warranty issues are different dealership to dealership. We haven't had any issues on our shop car, but that's not to say you won't.

There are laws out there to protect the consumer with their rights to aftermarket parts vs. warranty work, but I won't go into them here.

That's the normal line of reasoning. I was curious as to how BMW has reacted in the past to these types of mods. Technically, they have to prove that the issue with your car was caused by the mod (as far as i know) to deny your warranty claim. They can't legally deny your malfunctioning sunroof because you have an intake, but if your car has other issues with the engine, who's to say they wont see a mod and simply say it was the culprit. That's when the lawyers come to play, which few want to bother with (and I think car companies/dealers bank on).

See this alot with the mustang community. As he said, it varies from dealer to dealer also. Some are looking to void any warranty claim if they see a mod while others are much more 'friendly' to modified cars.

AFAIK, because the cat's main purpose is to make the exhaust "cleaner," it doesn't affect the sound nearly as much as the muffler. From what I've seen on YouTube it seems to make the exhaust throatier more than anything else. The goal of removing the cat is to improve the flow of the exhaust. The catless pipe will be louder than the HFC.

Edit: This is from the stage1 thread:

The main difference between Catless and HFC is that the HFC still tries to pass emissions standards. Therefore it sacrifices some performance gains to make it semi-streetable.

So long as the downpipe doesn't throw codes and your exhaust can pass emissions, you should be okay. IF you're caught though... well good luck.

Anyways, if you're going WOT past a cop in an exhaust modified (even the M-Perf exhaust) 335i then you're probably going to get pulled over with or without the modified downpipe.

As always - correct me if I'm wrong. I'm still a novice in this arena.

Just to see if I am on the same page, the catless down pipe (smaller looking downpipe) would be louder but less expensive; while the HFC down pipe (bigger looking DP) which is more money, will be less loud and more likely to pass a SMOG, is this correct?

I guess because it would be not as loud and more likely to pass SMOG, I think I am leaning to the HFC...

I ordered the HFC. They're saying its only about a 5hp difference b/t the two which isn't a big deal. I went catless on my last turbo car and have a bad taste in my mouth from that experience so I think this will be perfect.

Just to see if I am on the same page, the catless down pipe (smaller looking downpipe) would be louder but less expensive; while the HFC down pipe (bigger looking DP) which is more money, will be less loud and more likely to pass a SMOG, is this correct?

I guess because it would be not as loud and more likely to pass SMOG, I think I am leaning to the HFC...

Yeah, it's less expensive, smaller and has more performance because there is nothing in it. The other one they have to add stuff to try and meet the emission standards and that costs time/money.

Unless it's a track car or your car is somehow 8+ (or whatever it is) years old, then just get the HFC.